i) Field of the Invention
This invention relates to valves particularly though not solely for inclusion in the breathing circuit of a respirator.
ii) Summary of the Prior Art
A medical breathing circuit such as might be used in a Continuous Positive Airway Pressure Respirator (CPAP) includes an inspiratory gases tube which has one end thereof connected to the patient through an interface. For example through an endotracheal breathing tube extending into the trachea and ending just above the lungs. The other end thereof is connected to a respirator providing pressurised gases. The connection to the respirator may be direct or a self contained humidifier may be interposed.
One disadvantage of CPAP treatment is that it effectively reverses the normal breathing function. The patient has to relax to breath in and requires effort to breath out. Since normal breathing requires the exact opposite, the use of CPAP is sometimes difficult initially.
A number of devices exist to reduce the effort required by the patient to exhale. For example U.S. Pat. No. 5,657,752 assigned to Airways Associates describes a variable orifice venting aperture member in the nasal mask to help vent the exhalations. U.S. Pat. No. 5,065,756 assigned to New York University includes vent holes in the face mask for rapid discharge of exhaled air. U.S. Pat. 4,655,213 assigned to New York University includes a threshold valve to release air from the mask. Alternatively electronic methods exist such as that described in U.S. Pat. 5,803,065 assigned to Respironics have been used to improve the effectiveness of CPAP therapy.
However to some degree these existing devices are still somewhat ineffective. Also in some cases these apparatus include a bulky face mask and strapping which may be uncomfortable for the user.